1. Field of the Invention
Non-immunogenic polypeptides.
2. Description of the Prior Art
The use of polypeptides in circulatory systems for the purpose of engendering a particular physiological response is well known in the medicinal arts. Among the best known polypeptides utilized for this purpose is insulin which is used in the treatment of diabetes. Another group of polypeptides to which great therapeutic potential has been attributed are enzymes of the various classes. The principal factor which has severely limited the use in therapeutics of polypeptides in particular, enzymes, has been the fact that most of these compounds elicit an immunogenic response in the circulatory system. This response being the production of antibodies to the polypeptides by the circulatory system into which they are injected. This effect has one or both of two secondary consequences. The first being the destruction of polypeptides by the antibodies so called forth, or, the second more seriously, the appearance of an allergic response.
The destruction of the polypeptide by the antibodies is believed to be responsible for the rather low residence time of insulin in the human circulatory system, hence, persons afflicted with diabetes are forced to inject themselves fairly frequently with fresh doses of insulin. In the case of enzymes not only is there a problem of destruction of the polypeptide and the subsequent negation of its physiological activity but also the most undesired elicitation of an allergic reaction.
If it were found possible to so modify polypeptides that their desired physiological activity was maintained totally or at least in substantial proportion and at the same time no immunogenic response was generated within the circulatory system, then it would be possible to utilize these most valuable compounds in the mammalian circulatory system without the aforementioned disadvantages and in the far smaller amounts than has heretofore been possible.
The problems set forth hereinabove are well recognized and various approaches have been taken in attempts to solve them. The attachment of enzymes to insoluble supports has been the subject of a great deal of work. Reviews dealing with this subject will be found in Silman and Katchalski, Ann. Rev. Biochem., 35, 873 (1966), and Goldstein, Fermentation Advances, Academic Press, New York (1969) page 391. This approach however while of academic interest does not provide injectable long-life polypeptides. Another approach which has been taken to provide polypeptides of lengthened in vivo life has been the micro incapsulation of enzymes which has been discussed in numerous articles by Chang and co-workers, namely, Science, 146, 524 (1964); Trans. Am. Soc., 12, 13 (1966); Nature, 218, 243 (1968); Can. J. Physiol. Pharmacol., 47, 1043 (1969); Canad. J. Physiol. Pharmacol., 45, 705 (1967). A further approach lay in the heat stabilization of enzymes by attaching carboxy methylcellulose to an enzyme such as Trypsin (Mitz and Summaria, Nature, 189, 576 (1961) and the attachment of proteases to hydrophilic carriers (Brummer, et al, Eur. J. Biochem., 25, 129 (1972). These approaches however do not provide the polypeptides in a soluble form which is the most desirable for injection and dosage control of injectable materials. A further approach has been the attachment of synthetic polymers to polypeptidal proteins. A review of this work will be found in Sela, "Advances in Immunology", 5, 30, (1966) Academic Press, New York. In this work, it has been shown that while homopolymers of amino acids are nearly all non-immunogenic, when these polymers are attached to immunogenic proteins the immunogenic activity is not masked and antibodies are produced in test circulatory systems. For example, while polyglycine itself is non-immunogenic, when attached to a protein that conjugated protein becomes a hapten. Similarly while dextran itself is slightly immunogenic when coupled to insulin the insulin-dextran coupled material is believed to become substantially immunogenic.